1. Field of the Invention
The present invention relates to a switching device for switching on and off by operation of an operation knob which swings, and more particularly to a waterproof-type switching device capable of preventing water from entering into its case.
2. Description of Related Art
FIG. 6 is a side view schematically showing a structure of a conventional switching device 50 used in a window open/close system (power window system) of a vehicle. The switching device 50 has a case 51, and switches, a circuit board and other components which will be described later are accommodated inside the case 51. A seesaw-motion type operation knob 56 of a window open/close switch is operated to open and close a window of the vehicle. The operation knob 56 has an operation section 56a, a cap section 56b formed integrally with the operation section 56a, and holes 56c formed on the side walls of the cap section 56b. A cylinder 57 is provided on an upper surface 51e of the case 51, and a shaft 57a is formed integrally with the outer wall of the cylinder 57. The cap section 56b of the operation knob 56 is attached to the cylinder 57 from above, and the holes 56c of the operation knob 56 are brought into engagement with the shaft 57a of the cylinder 57. By this engagement, the operation knob 56 is supported by the cylinder 57 such that the operation knob 56 can swing around the shaft 57a. An operation knob 54 is a push-lock-type operation knob of a window lock switch, and is operated to lock the windows of the vehicle such that the windows cannot be opened, and to release the lock. The switching device 50 is attached to an arm rest (not shown) provided on the door of the driver's seat of the vehicle, and is covered by a cover 61 shown in FIG. 7 in areas other than the positions of the operation knobs 54 and 56.
FIG. 7 is a cross-sectional view showing a main part of the switching device 50 to which the cover 61 is attached. As apparent from the figure, the cylinder 57 is a hollow cylinder which is open to above and below to communicate with the inside of the case 51. A circuit board 64 is provided inside the case 51, and a switch 63 is packaged on the circuit board 64. The switch 63 is a switch for opening and closing a window, and is formed by a known slide switch. The switch 63 has an actuator 63a. An operation bar 62 connected to the operation knob 56 extends through a lower opening 57c of the cylinder 57 toward the inside of the case 51. A concave 62a is formed at the lower end of the operation bar 62. By engagement between the concave 62a and the actuator 63a of the switch 63, the motion of the operation knob 56 is transmitted through the operation bar 62 to the switch 63, and contacts equipped inside the switch 63 are switched between on and off in accordance with the operating position of the operation knob 56. A point Q is the rotation center of the operation knob 56, and corresponds to the position of the shaft 57a shown in FIG. 6. An opening 61a through which the finger is inserted to operate the operation section 56a of the operation knob 56 is formed on the cover 61. The operation section 56a is exposed through the opening 61a. 
A switching device having a similar structure as that of the switching device 50 explained above is shown in JP-A-8-180755 and JP-A-5-314864 (Patent References 1 and 2). JP-A-11-86662 (Patent Reference 3) discloses a switching device which is waterproofed by surrounding soldered portions of electronic component terminals on a circuit board with side walls formed by rubber contact members without requiring coatings.
In the switching device 50 described above, the opening 61a of the cover 61 is sized large enough to prevent any trouble which may be caused when putting the finger on the operation section 56a of the operation knob 56 to lower or raise the operation section 56a. As a result, raindrops entering through the window which has been left open, beverage accidentally spilt in the vehicle compartment or the like (hereinafter collectively referred to as “water”) may flow through the opening 61a into a concave 61b as illustrated in FIG. 7. In this case, when a large amount of water flows into the concave 61b, the water entering the concave 61b flows through a clearance 65 formed between a bottom wall 61f of the concave 61b and the cap section 56b of the operation knob 56 and rises through a clearance 66 formed between the cap section 56b of the operation knob 56 and a side wall 57e of the cylinder 57. Then, the water enters through an upper opening 57b of the cylinder 57 into the cylinder 57, and flows through the lower opening 57c of the cylinder 57 into the case 51 as shown by arrows in FIG. 7.
Nothing is described about prevention of water which enters from below the operation knob 56 as in the manner explained above in Patent References 1 and 2 mentioned above. Additionally, while Patent Reference 3 discloses a waterproofing technique for preventing short-circuit, entrance of water from below the operation knob into the case cannot be prevented in such a switching device which does not use rubber contacts according to the technique shown in this reference.